1. Field of the Invention
The present invention relates to a process for drawing plastic laminates. More particularly, the present invention relates to a process for drawing plastic laminates comprising an ethylene terephthalate type polyester layer and a gas barrier layer of an olefinvinyl alcohol copolymer, said two layers being bonded through an adhesive layer. Furthermore, the present invention relates to a draw-formed structure.
2. Description of the Prior Art
Since polyethylene terephthalate (PET) is excellent in the moldability and can be molecularly biaxially oriented, PET is used as a biaxially drawn film, thermoformed cup or biaxially draw-blow-formed bottle excellent in the impact resistance, rigidity, gas barrier property and transparency. However, the gas permeability of this polyester, for example, the oxygen or carbon dioxide gas permeability, cannot be neglected, and in the field of films, a biaxially drawn PET film is laminated with other high barrier film through an adhesive and this laminate is used for the production of a pouch. In the field of thermoformed PET cups, a drawn and oriented cup having a capacity of 200 to 300 milliliters is used for storing beer or carbonated drink, but since the storability is very low, cups of this type are not broadly used. In the field of biaxially draw-blow-formed PET bottles, the shelf life is about 3 months and practically satisfactory because of the relation between the inner volume of the vessel and the surface area of the vessel when the bottle size is large and the capacity is larger than 1 liter. However, in case of a small-size bottle having a capacity smaller than 1 liter, especially smaller than 500 milliliter, the shelf life is about 2 months at longest and the use of this bottle is considerably limited.
An olefin-vinyl alcohol copolymer such as a saponified ethylene-vinyl acetate copolymer is well-known as a heat-moldable resin excellent in the oxygen barrier property, and it also is known that this resin is combined with other resin excellent in the moisture resistance, for example, an olefin resin, and is used for the production of an undrawn or drawn multi-layer plastic vessel.
Proposals have been made as to the production of vessels from laminates of a polyester and an olefin-vinyl alcohol copolymer. It is naturally expected that a laminate of this type will be excellent in the gas barrier property, impact resistance and rigidity, but a laminate of this type, especially a drawn laminate, has not been practically used. One reason is that an excellent adhesive providing a strong interlaminar bonding between the polyester and olefin-vinyl alcohol copolymer even after draw forming has not been found out. Reduction of the interlaminar bonding strength by draw forming cannot be avoided and the most important reason is that means capable of controlling this reduction of the interlaminar bonding strength to a very low level has not been developed.